Method of producing semi-hard magnetic ni-cu-fe alloys and the resulting product

ABSTRACT

1. A METHOD OF PRODUCING A SEMI-HARD MAGNETIC IRON BASE ALLOY ARTICLE COMPRISING: PROVIDING AN ALLOY BODY FREE OF ALUMINUM AND TITANIUM AND CONSISTING ESSENTIALLY OF FROM 12 TO 25% BY WEIGHT OF NICKEL, 3 TO 20% BY WEIGHT OF COPPER AND THE REMAINDER IRON AND SMALL AMOUNTS OF INCIDENTAL IMPURITIES; ANNEALING SAID ALLOY BODY AT A TEMPERATURE OF FROM 500* TO 650*C. FOR A TIME DURATION OF FROM 1/2 TO 6 HOURS; AND COLD WORKING THE ANNEALED ALLOY BODY IN A GIVEN DIRECTION SUFFICIENTLY TO REDUCE THE AREA THEREOF FROM 10 TO 80% TO INCREASE THE RESIDUAL MAGNETIC FLUX DENSITY IN SAID GIVEN DIRECTION OF THE COLD-WORKED ALLOY BODY TO AT LEAST ABOUT 10.5 KILOGAUSSES AND ESTABLISH THEREIN A SUBSTANTIALLY RECTANGULAR HYSTERESIS LOOP CHARACTERISTIC AND IMPART THERETO A COERCIVE FORCE OF FROM 20 TO 80 OERSTEDS, AND HARDNESS NOT GREATER THAN 400 ON THE VICKERS HARDNESS SCALE.

Nov. 5, 1974 Filed May 22, 1972 Coercive Force He in Oersteds in Oersteds YOZO NAKAJIMA ETA!- 3 METHOD OF PRODUCING SEMI-HARD MAGNETIC N1Cu.Fe ALLOYS AND THE RESULTING PRODUCT 2 Sheets-Sheet 2 l l l l l l l I Content of Copper in FIG. 4

L l l l I Content of Nickel in% United States Patent 3,846,185 METHOD OF PRODUCING SEMI-HARD MAG- NETIC Ni-Cu-Fe ALLOYS AND THE RESULT- IN G PRODUCT Yozo Nakajima and Shohei Ohtani, Sagamihara, Japan, assignors to Mitsubishi Denki Kabushiki Kaisha, Tokyo, Ja an Cont i nuation-in-part of abandoned application Ser. No. 855,117, Sept. 4, 1969. This application May 22, 1972, Ser. No. 255,723

Claims priority, application Japan, Sept. 11, 1968, 43/ 65,438 Int. Cl. H01f 1 /00 US. Cl. 148-120 4 Claims ABSTRACT OF THE DISCLOSURE The present invention pertains to a method of producing semi-hard magnetic ternary alloys and to products produced by such a method. In accordance with the method of the present invention, a ternary alloy composed of from 12 to 25% nickel, 3 to 20% copper and the remainder iron is first annealed at a temperature of 500 to 650 C. for a time duration of from /2 to 6 hours and then the annealed ternary alloy body is cold-worked to effect an area reduction of from 10 to 80% thereby increasing the residual magnetic flux density in the direction of cold-working and establishing in the magnetic body a substantially rectangular hysteresis loop characteristic. The ternary alloy does not contain aluminum, titanium or any element which affects to any degree the magnetic or mechanical properties of the alloy and consequently the alloy may be easily machined and surface plated.

This is a Continuation-in-Part of Application Ser. No. 855,117 filed on Sept. 4, 1969 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to semi-hard magnetic nickelcopper-iron ternary alloys suitable for use in electromagnetic relays and hysteresis motors and to a method of manufacturing the same.

There are already known semi-hard magnetic alloys including cobalt-iron alloys, special steels, and iron base alloys containing aluminium and titanium. Such alloys are disadvantageous in that they contain expensive ingredients and are difiicult to mechanically work due to their brittleness and hardness. Also some of the semi-hard magnetic alloys heretofore employed contain some chemically active elements and the presence of such elements greatly increases the difficulty of controlling the manufacturing process of producing them since care must be taken to prevent the occurrence of unwanted chemical reactions. Another type of half-hard magnetic iron base alloys has been proposed for use in electromagnetic devices containing nickel and copper in such amounts that the flux density due to the iron involved does not decrease too much while the coercive force is maintained at an appropriate magnitude. These latter alloys are advantage- Ous in that they contain only inexpensive ingredients, the alloys are stable in characteristics because of the absence of chemically active elements, and they are easily mechanically worked due to their ductility at room temperature. The conventional processes of producing such alloys have been, in most cases, to quench the alloys containing the specified ingredients from an elevated temperature above 800 C., then suitably precipitate the nonmagnetic phase by a high cold working or annealing treatment and magnetically harden the alloy thus processed to impart the desired semi-hard magnetic characteristics to the lat- 'ice ter. Semi-hard magnets formed of the conventional nickelcopper-iron alloys of the type as above described have typically had such magnetic properties that for an alloy including, by weight, 16% of nickel, 3% of copper and the balance iron, the coercive force H is about 30 oersteds and the residual magnetic flux density B is about 12 kilogausses with the hysteresis loop insufficient in squareness.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention to provide nickel-copper-iron ternary alloys having improved magnetic characteristics belonging to the category of the semihard magnetic alloys.

It is a further object of the invention to provide improved semi-hard magnetic nickel-copper-iron ternary alloys having an increased residual magnetic flux density with the coercive force in the order of 40 oersteds and having its hysteresis loop improved in squareness.

It is another object of the invention to provide a method of producing semi-hard magnetic nickel-copper-iron ternary alloys of the type having the characteristics described in the two foregoing paragraphs.

The invention accomplishes the above cited objects by the provision of a method of producing a semi-hard magnetic iron base ternary alloy by providing an alloy body containing from 12 to 25% by weight of nickel, from 3 to 20% by weight of copper and the balance iron and small amounts of incidental impurities, annealing the alloy body at a temperature of from 500 to 650 C. for a time of from /2 to 6 hours and preferably from 2 to 4 hours, and cold working the annealed body to a reduction of area of from 10 to to thereby increase the residual magnetic flux density in the working of the resulting body while providing a good rectangular hysteresis loop. The cold working may be preferably either a cold reduction or a wire drawing.

In order to render ingots of the alloy sound and to smoothly work the bodies of the alloy after having been processed according to the invention, at least one of the elements manganese, silicon and vanadium may be added in small amounts to the alloys upon melting them for the purposes of deoxidation and desulfurization.

Also for the purpose of controlling the coercive force of the resulting body of the alloy and improving the squareness of the resulting hysteresis loop, the cold reduced body of the alloy may be additionally annealed at a low temperature of from 200 to 450 C.

BRIEF DESCRIPTION OF THE DRAWING The invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a graph illustrating changes in magnetic properties of a 16% Nil0% Cu Fe alloy plotted against its annealing temperature;

FIG. 2 is a graph illustrating the effect of cold reduction upon the coercive force and residual flux density for Ni-Cu-Fe alloys processed in accordance with the invention and annealed at two specific annealing temperatures;

FIG. 3 is a graph illustrating the relationship between the content of copper and the coercive force for the alloys of the invention with a parameter being a content of nickel; and

FIG. 4 is a view similar to FIG. 3 but illustrating the relationship between the content of nickel and the coercive force.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is characterized by the unique combination of an annealing process and a succeeding cold reduction process effected in the step of finishing the alloy product having the desired excellent magnetic characteristics. In accordance with the invention, from 12 to 25% by weight of nickel (Ni), from 3 to 20% by weight of copper (Cu) and from 55 to 85% by weight of iron (Fe) are first melted in an induction furnace having an open atomsphere to provide a ternary alloy body in the form of an ingot. It has been found that such raw materials of commerical grade including small amounts of incidental impurities can be used with the satisfactory results. For example, 16% by weight of nickel, by weight of copper and the balance iron and small amounts of incidental impurities were melted in an induction furnace such as above described and cast into an ingot of alloy having a weight of about 10 kilograms. The incidental impurities which may be present are those not detrimentally affecting the desired properties of the resulting product and for example, aluminum and titanium should not be present since these elements render the resulting product too hard and brittle. Then the ingot was forged and rolled into plates about 3 millimeters thick at a temperature of from 600 to 1,000 C. The rolled plate was subjected to a cold reduction operation and formed into sheets having a thickness of 1 millimeter.

Samples cut out from the sheets thus prepared were annealed for a predetermined time, for example one hour, at various temperatures, including both the particular temperature at which the sheets had been completed to be rolled and 700 C., and then their magnetic properties were determined. The results of the determination are listed in Table I as will be described hereinafter.

Referring now to FIG. 1 of the drawings, there is il lustrated the relationship between magnetic properties along the ordinates and the annealing temperature along the abscissa of the special alloy as above described. The

magnetic properties are typically represented by the residual magnetic flux density B, in kilogausses, the coercive force H in oersteds and the squareness ratio of the hysteresis loop. The samples were annealed at the indicated temperature for 1 hour. Dotted curve labeled B, is a plot of the residual flux density against the annealing temperature and solid curve labelled Hg is a plot of the coercive force against the annealing temperature Another dotted curve labelled B /B is a plot of the squareness ratio against the annealing temperature Where B represents the saturated magnetic flux density of the sample magnetized in a magnetic field of 200 oersteds and B represents the corresponding residual magnetic flux density exhibited by the same sample progressively demagnetized from 200 oersteds.

From FIG. 1 it is seen that as the annealing temperature increases, the coercive force H first decreases to a minimum value at about 450 C. Then the coercive force rapidly increases at annealing temperatures about 500 C. until it reaches a maximum value between 550 and about 580 C. Thereafter the coercive force decreases but remains considerably high up to about 650 C. However the residual flux density B changes in the reverse sense from the coercive force with an increase in annealing temperature.

It is noted that the samples annealed at about 580 C. were very low in residual flux density. For example, a sample annealed at 550 C. for one hour had a residual flux density B of 3.9 kilogausses, a coercive force H of 94 oersteds and a squareness ratio B /B of 0.89. On the other hand, if it is attempted to impart a coercive force H above 40 oersteds to a particular half hard magnetic alloy of the conventional Ni-Cu-Fe system as annealed under the same conditions, then its residual flux density B, could amount to only 12.5 kilogausses. Moreover, even if the coercive force is reduced to 30 oersteds, the corresponding B could only increase to 14.5 kilogausses.

From the foregoing it will be appreciated that the alloys annealed in accordance with the invention are very low in residual flux density but far higher in coercive force as compared with the prior art practice.

It has been found that an annealing temperature of from 500 to 650 C. gives the most satisfactory results. Generally, the higher the annealing temperature the shorter the annealing time will be and vice versa. It has been also found that with the satisfactory results, the annealing time should range from /2 to 6 hours and preferably from 2 to 4 hours.

It has been unexpectedly found that the present alloys annealed in the manner as above described undergo a substantial increase in residual flux density through a special cold reduction according to the invention. For example, the sample annealed at 550 C. for one hour as above described was cold rolled to a reduction of area of The rolled sample had excellent semi-hard magnetic properties such that the residual flux density and coercive force were respectively of 14.9 kilogausses and oersteds in the rolling direction with the squareness ratio equal to 0.99 as shown in the following Table I.

TABLE I.MAGNETIC IIROPERTIES OF ALLOY A OF THE From Table I it is seen that with the coercive force reduced to about 30 oersteds, the corresponding residual flux density further increased to a value of 16.7 kilogausses with the squareness ratio equal to 0.97. It is believed that this unexpected great increase in residual flux density results from the formation of magnetic anistropy in the material of the cold rolled sheets although the exact mechanism therefor is not yet known.

Thus it will be appreciated that the invention is characterized by a unique combination of an annealing treatment effected under a condition to increase the coercive force with the residual flux density disregarded and the succeeding cold working or reduction serving to increase the residual flux density and therefore the squareness of hysteresis loop in the rolling direction while the coercive force is allowed to decrease somewhat resulting in an alloy having excellent semi-hard magnetic properties. This has not been known prior to the present invention.

In order to determine an operable range of reduction rates required to attain the desired purpose, many experiments were conducted. The results thereof are illustrated in FIG. 2 wherein the residual flux density B, in kilogausses and the coercive force H. in oersteds are plotted along the ordinate and the reduction rate in percent is plotted along the abscissa. Curves labelled B, and H plot the residual flux density and coercive force against the reduction rate and the solid curve depicts samples annealed at 550 C. for one hour and the dotted line depicts those annealed at 600 C. for one hour.

From FIG. 2 it is seen that an increase in the reduc tion rate is generally accompanied by an increase in the residual flux density but by a decrease in the coercive force. It is to be noted that with the reduction rate exceeding a certain value, the coercive force not only decreases but the residual flux density also does not increase. Thus it has found that the optimum range of reduction rates should be from 10 to although such depends upon the annealing condition.

The composition of the present alloys will now be described. Many experiments were conducted with various iron base alloys including either one of copper and nickel in different contents with the other element remaining at a fixed content. After having been annealed at 550 C. for one hour, the alloys exhibited coercive forces as illustrated in FIGS. 3 and 4 wherein the coercive force H in oersteds is represented along the ordinates and the content of copper or nickel in percent by weight is represented along the abscissas respectively. More specifically, FIG. 3 illustrates two series of the alloys containing various amounts of copper with the content of nickel maintained at 15 and 20% by weight respectively while FIG. 4 illustrates two series of alloys containing various amounts of nickel with the content of copper maintained at 5 and by weight.

In accordance with the invention, the alloys as annealed are required to have a coercive force equal to or more than 40 oersteds. To this end, the alloys must include copper in an amount not less than 3% and nickel in an amount not less than 12% on the basis of the Weight of the alloy as will be readily understood from FIGS. 3 and 4. Also, the nickel should have the upper limit of its contents not more than 25% by weight. On the other hand, the upper limit of the content of copper depends upon the content of nickel simultaneously present in the alloy but it should not exceed 20% on the basis of the total weight of the alloy for the reason that a content of copper exceeding 20% renders the resulting alloys difficult to hot work in the process of forming them into desired products.

Many iron base alloys have been prepared containing nickel and copper in difierent contents all falling within the limits as above specified and treated in the manner 3 as previously described and formed into sheet articles.

The resulting sheets exhibited the magnetic properties listed in the following Table II. Table II also lists the compositions and treating conditions of the alloys and B and H represent the point on the demagnetization curve giving the maximum energy product.

TABLE III.HARDNESS OF PRESENT ALLOYS ON VICKERS HARDNESS SCALE From above Table IE, it can be readily seen that the alloys of the present invention have a hardness no greater than 400 on the Vickers hardness scale and thus semihard magnetic alloys may be manufactured in accordance with the present invention which eliminate the disadvantages of the prior art type alloys.

Thus it may be appreciated that the alloys of the pres- 0 ent invention are particularly suitable for use as magnetic cores for latching relays and other electromagnetic devices. It has been the practice in the art to work the alloy body into a suitable shape tor a magnetic core and then heat treat the core body whereas the present invention directly produces magnetic cores as the resulting product. This is due to the comparatively low hardness of the semi- TABLE II.-MAGNETIC PROPERTIES OF ALLOYS OF THE INVENTION Magnetic properties Reduc- Composition tion Br 1n B1, in in weight ratio, kilo- H m kilo- Hm in percent Annealed 2115- percent gansses oersteds Br/BZDO gausses oersteds Notation of heat:

B 15Ni-4Cu-Fe 550C. for lhour 23 12,12 El 31 1% 25 13.3 48 0.94 11.8 42 C 12N1-6Cu-Fe -...--do 45 15,0 35 0. 96 13.9 31 D 15Ni-6Cu-Fe do 25 13.0 43 0.94 11.6 38 15 11. 4 70 0. 94 9. 7 59 E 15Ni-8Gu-Fe do 45 14.0 48 0.95 12.2 44

a as a: o 12.2 F 16m 20 F 550 1 s5 14.6 46 0.98 13.7 43 -1 I 9 25 13 6 46 0.94 12.5 42 G HEN-15C F 40 11.1 75 0.97 9.8 67

1- ue 550 0- f 1 r------{ 60 56 8.92 11.3 60 ll. 2 58 9 10. H 40 13. 1 39 o. 97 12. 0 as I. 21Nl-60u-Fe 50 13. 7 42 0. 98 12. 8 39 J 21N1-80u-Fe 80 13.6 42 0. 96 12. 1 37 I I' 20 13.3 44 0.97 12.6 40 e 30 16.1 29 0.98 14.8 26 530 C. for 4 hours 40 12.9 45 0. 94 11.2 36 M. 16Ni-5Cu-Fe do 14.3 41 0.93 12.9 36 580 C. for 1 hour 30 15. 4 37 0. 93 14. 0 33 Semi-hard alloy systems are known which include nickel, copper, iron and small amounts of aluminum and titanium, but these alloys are difiicult to produce since the raw materials do not easily melt together and the resulting alloy is very diflicult to plate. Moreover, due to the presence of aluminum and titanium, the alloy has a Vickers hardness of approximately 600 and therefore these alloys may not easily be cut or pressed into the desired machine parts.

The ternary alloys of the present invention are not nearly as hard as such prior art alloy because of the absence of titanium and aluminum. The alloy of the present invention has a Vickers hardness no greater than 400 after cold-rolling and the following Table III gives the Vickers hardness number for the various heats listed in Table II of the present specification.

hard alloys which enables them to be cleaned, straightened, and machined in a simple manner.

While the invention has been described in conjunction with sheet articles, it is to be understood that the same is equally applicable to wire articles and other shaped articles. Thus an ingot of iron base alloy containing 16% Ni and 6% Cu was wire drawn with a reduction rate of 50% The resulting wire article was annealed at 550 C. for one hour and then drawn into a diameter of 0.55 mm. with a reduction ratio of 50%. The wire article thus prepared exhibited a residual flux density of 14.5 kilogausses and a coercive force of 45 oersteds. When the wire article was increased in straightness by a suitable mechanical straightening treatment, its residual flux density increased to 15.6 kilogausses while its coercive force decreased to 37 oersteds. This means that plastic deformation occurred in the wire article during the straightening operation and such gives the same result as does an increase in working or reduction rate.

From Table II it will be appreciated that an increase in reduction rate causes a decrease in coercive force. It has been found that, in addition to increasing the particular reduction rate, an additional final annealing effected at a temperature of 400 C. or less is also effective for providing a low coercive force not higher than 30 oersteds. For example, a sheet article produced from an iron base alloy containing 16% Ni and 6% Cu was annealed at 550 C. for one hour and then cold reduced at different rates, and the results obtained are illustrated in the following Table IV.

TABLE IV What we claim is:

1. A method of producing a semi-hard magnetic iron base alloy article comprising: providing an alloy body free of aluminum and titanium and consisting essentially of from 12 to by weight of nickel, 3 to 20% by Weight of copper and the remainder iron and small amounts of incidental impurities; annealing said alloy body at a temperature of from 500 to 650 C. for a time duration of from /2 to 6 hours; and cold working the annealed alloy body in a given direction sufiiciently to reduce the area thereof from 10 to 80% to increase the residual magnetic flux density in said given direction of the cold-worked alloy body to at least about 10.5 kilogausses and establish therein a substantially rectangular Magnetic properties 01 IGNi-GCu-Fe alloy as differently cold reduced Succeeding cold reductions with Then the samples cold reduced with the reduction rates of 60 and 80% were annealed at various low temperatures between 200 and 500 C. for different periods of time. The resulting magnetic properties are listed in the following Table V.

TABLE V Magnetic properties of 16Ni-6Cu-Fe alloy after having been annealed at low temperatures From the above Table V, it may be seen that the additional annealing step effected at a temperature not higher than 450 C. is effective for improving the magnetic properties which were deteriorated by excessive reduction such that the residual flux density B, increased and therefore the hysteresis loop is improved in squareness while the coercive force decreases.

As previously described, the invention can be practiced starting with raw materials of the commercial grade including small amounts of incidental impurities. Also the addition of manganese (Mn), silicon (Si) and/or vanadium (V) may be added in small amounts to the alloys upon melting them for the purpose of deoxidation and desulfurization without essentially affecting the magnetic properties of the resulting alloys. The addition of such elements is effective for rendering the ingots of alloys sound and for permitting the present alloys to be smoothly worked into the desired products,

hysteresis loop characteristic and impart thereto a coercive force of from 20 to oersteds, and hardness not greater than 400 on the Vickers hardness scale.

2. A method according to Claim 1; wherein said annealing step comprises annealing said alloy body at a temperature of from 500 to 650 C. for a time duration of from 2 to 4 hours.

3. A method according to Claim 1; further comprising annealing the cold-worked alloy body within a temperature range of from 200 to 450 C. for a time dura tion sufficient to render the substantially rectangular hysteresis loop characteristic more square and to decrease the coercive force of the resulting alloy body.

4. A semi-hard magnetic iron base alloy article free of aluminum and titanium and consisting essentially of from 12 to 25% by weight of nickel, from 3 to 20% by weight of copper and the remainder iron and small amounts of incidental impurities and having a hardness not greater than 400 on the Vickers hardness scale, a squareness ratio of at least for the hysteresis loop characteristic thereof, a residual flux density of at least about 10.5 kilogausses and a coercive force of from 20 to 80 oersteds.

References Cited UNITED STATES PATENTS 2,167,188 7/1939 Schaarwachter et al. 148102 1,987,468 1/1935 Dahl et al 148120 2,196,824 4/ 1940 Dahl et al. 148-31.57 3,574,003 4/1971 Nara et al 148-120 2,114,183 4/1938 Haase et al. 148-120 WALTER R. SATTERFIELD, Primary Examiner U.S. Cl. X.R. 

1. A METHOD OF PRODUCING A SEMI-HARD MAGNETIC IRON BASE ALLOY ARTICLE COMPRISING: PROVIDING AN ALLOY BODY FREE OF ALUMINUM AND TITANIUM AND CONSISTING ESSENTIALLY OF FROM 12 TO 25% BY WEIGHT OF NICKEL, 3 TO 20% BY WEIGHT OF COPPER AND THE REMAINDER IRON AND SMALL AMOUNTS OF INCIDENTAL IMPURITIES; ANNEALING SAID ALLOY BODY AT A TEMPERATURE OF FROM 500* TO 650*C. FOR A TIME DURATION OF FROM 1/2 TO 6 HOURS; AND COLD WORKING THE ANNEALED ALLOY BODY IN A GIVEN DIRECTION SUFFICIENTLY TO REDUCE THE AREA THEREOF FROM 10 TO 80% TO INCREASE THE RESIDUAL MAGNETIC FLUX DENSITY IN SAID GIVEN DIRECTION OF THE COLD-WORKED ALLOY BODY TO AT LEAST ABOUT 10.5 KILOGAUSSES AND ESTABLISH THEREIN A SUBSTANTIALLY RECTANGULAR HYSTERESIS LOOP CHARACTERISTIC AND IMPART THERETO A COERCIVE FORCE OF FROM 20 TO 80 OERSTEDS, AND HARDNESS NOT GREATER THAN 400 ON THE VICKERS HARDNESS SCALE. 